Communication systems and satellite navigation systems often need spectrum analyzers. Swept spectrum analyzers have been in use for many years, because they are less complex compared to FFT (Fast Fourier Transform) spectrum analyzers. Some analyzers have both analog and digital signal processing means.
U.S. Pat. No. 6,700,366, entitled “Very fast swept spectrum analyzer”, describes a system in which the signal spectrum is formed by mixing a ramping local oscillator and an input signal to generate an IF signal, the resulting IF (Intermediate Frequency) signal having a phase change with respect to the input signal, the phase change including a quadratic portion. For analysis, the IF signal is processed such that the quadratic component of the phase change is removed. IF processing circuitry includes a resolution bandwidth filter and an analog-to-digital converter.
U.S. Pat. No. 6,275,020, entitled “Frequency analysis method and sweep type spectrum analyzer”, describes a sweep type spectrum analyzer, where analyzing the frequency components included in the signal to be measured are based on the correspondence relation between a power of each of the intermediate frequency signals and a frequency of the main swept frequency signal, an inverse swept signal is multiplied by each intermediate frequency signal, the inverse swept signal being frequency-swept in the reverse direction to the frequency transition direction of the associated intermediate frequency signal, and a constant frequency component obtained from the results of the multiplications is extracted as a frequency spectrum.
U.S. Pat. No. 4,771,232, entitled “Non-interruptive spectrum analyzer for digital modems”, describes a system that provides extracting spectral data from the actual received modem signal, where multipliers are used in the digital frequency converter.
However, devices with analog components are not always stable and provide less accuracy compared to fully digital solutions. The present invention is intended as a simple system for full digital sweep type spectrum analysis with up/down frequency conversion, where analysis time is less than half compared to sweep type spectrum analyzers with only down frequency conversion. The system provides measurements of frequency spectrum of an input complex analog baseband signal without use of multiplication operations for frequency conversion.